The largest pen you can make is a circle with a circumference of 100 meters. Its diameter is 31.83 meters, and its area = 795.77 square meters. It's a lot easier to just go with a square ... the...
How is it largest ? Do you mean longest ? Do you mean widest ? There's no answer for either longest or widest. If you make it 1 foot wide, then it's 9 feet long, and if you make it 1 inch long, then...
Fencing can have 2 definitions: Those wooden/vinyl posts around your property, or fighting with long weapons (generally swords).
From the Online Etymology dictionary:
fence (v.)
"fight with swords,"...